Purpose: To perform a biomechanical comparison between an older established and a recently introduced technique, used in suturing semitendinosus quadrupled grafts.

Methods: Flexor tendons were harvested from pigs giving a tendon of similar dimensions to semitendinosus. Specimens were prepared using an older established suturing method utilising a Bunnel ‘whip’ stitch (group A, 21 specimens), and a recently introduced(1) method where the tendon is sutured back on itself having an overlap of either 20mm or 30mm and forming a closed loop (group B, 40 specimens). In group A, a tibial fixation button was used and grafts were prepared as to have a common representative overall length. Consideration was given in mounting either end of these grafts in representative conditions. The lengths of Group B specimens were of comparable dimensions to group A, but were mounted by using custom-made grips incorporating roller bars. Tests were performed in a Dartec servohydraulic materials testing machine in fatigue and in single loading at various strain rates and by using physiological loading patterns and in physiological ambient conditions.

Results: Group A specimens failed in a small load range of 200–250N and at the whipstitch, which snapped at the knot tied around the tibial button. Group B specimens failed either in the overlap region (for the shorter overlaps) or in mid-tendon substance (for longer overlaps). In general group A showed low fatigue strength and high unpredictability in its fatigue lifetime. Group B showed nearly 3 times as high fatigue strength and consistent predictable results throughout the range of loads used (200–600N).

Conclusion: The new technique for suturing quadrupled semitendinosus grafts has been evaluated in tests under more physiological loading and ambient conditions. The technique significantly improves the fatigue life of the graft and should permit the goal of a more aggressive rehabilitation programme.